The present invention relates generally to optical networking, and, more particularly, to installations in which a WDM ring carries short-haul communications.
There is currently a market need, experienced by, for example, telephone carriers and cable operators, to provide short-haul transmission of internet protocol (IP) packets among interconnected nodes that are typically spaced apart by about 20 km or less. Proposed systems use an IP packet over SONET interface, and use wavelength-division multiplexing (WDM) to carry the packets on an optical fiber transmission medium.
One particular class of architectures for the short-haul network is the class of ring architectures. Such architectures are especially useful for serving business parks, campuses, military bases, networks of geographically dispersed company buildings, and the like. Typically, a pair of counter-propagating fiber-optic rings connects a plurality of nodes, disposed along the ring, with a hub. The hub manages inbound and outbound transmissions between the ring and external communication networks. Each node typically serves one subscriber or aggregate of subscribers, which by way of illustration could be an office suite in an urban office building.
At each node, the ring is typically routed through an electronics cabinet where the received traffic for that node is extracted from the ring, and the transmitted traffic for that node is injected into the ring. The handling of such traffic, generally in the electrical domain, is typically carried out by a conventional packet data shelf, conjoined with a transceiver for performing conversions between the optical and electrical domains.
Between nodes, it is often possible to house the ring components within underground pipes or tunnels, or the like. However, to reach a node, it is often necessary to route the ring components from floor-to-floor within an office building, or to otherwise expose the ring to easier access. Such an arrangement has at least two disadvantages.
One disadvantage is that routing through a building is typically achieved by relaying all of the ring traffic from one patch panel to another as the ring rises or descends from floor to floor within the building. There is loss associated with each patch-panel connection. This loss is cumulative over all of the nodes through which the affected traffic passes. Each subscriber is penalized by the losses suffered not only in reaching its own node, but also in reaching each node through which that subscriber""s traffic passes.
A second disadvantage is that as it enters and exits a node, the ring may suffer reduced reliability and security, because it is more exposed to accidental disturbances as well as to deliberate tampering.
We have developed a dual-ring, bidirectional optical fiber transmission system that interconnects a plurality of nodes with a hub, such that multiple WDM channels are established on each ring.
An illustrative such system is described briefly below. Further details of the illustrative system can be found in the copending application of L. Adams, J. Anderson, W. Brinkman, and R. Broberg, filed on Jun. 15, 1999 under the title xe2x80x9cWideband Optical Packet Ring Network,xe2x80x9d and assigned to the same assignee as the present invention.
Although the invention is not so limited, it is particularly useful when a relatively wide spacing of the channels, exemplary a spacing on the order of 10-30 nm, and more typically about 20 nm, enables the use of very low cost transceivers and avoids the need for temperature control. Such a WDM system is often referred to as a coarse WDM (CWDM) system.
At each node, an optical add-drop module (OADM) comprises dielectric thin film filters (TFFs) arranged to (a) extract, for the purposes of a receiver, or (b) insert, for the purposes of a transmitter, information in one or more of the channels. In particular, this type of filter is well suited to accommodate the wavelength drift normally associated with temperature changes in the laser transceivers if they are uncooled.
We have observed that such use of TFFs in a C-WDM system offers a further advantage. Because the wavelength tuning of TFFs is generally highly humidity-stable and is relatively stable over a wide temperature range, and because the relatively large width of C-WDM channels can, in any event, accommodate significant amounts of temperature drift, the use of these filters relaxes the need to maintain the OADMs in a temperature-controlled environment, or even in an environment limited to habitable temperatures. In view of this, we have recognized, for the first time, that the OADM can be removed from the electronics cabinet that houses, e.g., the pertinent node""s packet processor. Instead, it can be placed physically nearer the less accessible portions, e.g., the underground portions, of the ring. This makes it possible to extract the traffic arriving for each node and to route solely the extracted traffic through the building where the pertinent subscriber is located. This exempts the traffic belonging to other subscribers from the patch-panel losses and public exposure suffered by the instant subscriber""s traffic.
Thus, in one aspect, the invention is a fiber-optic WDM ring for carrying communication traffic among a plurality of nodes, each node associated with respective subscriber premises. The WDM ring includes an OADM at each node for adding and dropping signals associated with that node. The WDM ring also includes powered terminal equipment at each node for conditioning incoming and outgoing data and for converting between the optical and electrical domains. The OADM at each of at least some nodes, to be referred to as enhanced nodes, is situated at a site physically separated from the powered terminal equipment, and is coupled to the powered terminal equipment via an optical medium. At each enhanced node, traffic not destined for that node is routed through no more than one enclosure on subscriber premises that requires a connection. If there is such enclosure, it contains the OADM.